In the application of liquid substances to a moving web or successive sheets of material, it is considered well known in the art to apply the liquid using a rotating transfer roller, and to directly apply the liquid uniformly onto the roller by means of a doctor blade assembly. The doctor blade assembly generally includes a reservoir chamber extending the length of the transfer roller and in contact with the circumferential surface thereof, and a pair of doctor blades extending longitudinally on either side of the chamber. The doctor blades are angled obliquely toward the transfer roller surface, and serve both to seal the reservoir chamber to the roller and to form a uniform film of liquid on the roller transfer surface. The assembly also must include some means to seal the reservoir chamber at the ends of the roller, so that the liquid is not flung from the roller into the surroundings, and so that the liquid may be pumped through the reservoir during the transfer process. Such transfer systems are used in flexographic and gravure printing, adhesive applicators in the paper converting industry, coating applicators in many different industrial processes, and the like. An exemplary system is described in U.S. Pat. No. 4,821,672, issued to Nick Bruno on Apr. 18, 1989.
Chambered doctor blade devices are generally employed with large printing presses or paper converting machines, either of which comprising a substantial capital investment. The forces of economics dictate that these machines be used productively to the greatest extent possible. Any downtime is considered to be a diminishment of return on investment, to be avoided whenever possible.
It is often necessary to change the ink or coating compound that is applied by the chambered doctor blade apparatus, due to color change or alteration of the machine setup. Typically, the ink reservoir, supply lines, valves, and inking chamber must be drained, flushed, cleaned, and resupplied with a new ink or coating compound. The time spent in carrying out these tasks comprises machine downtime, a loss in productivity. Automated systems for supplying a doctor blade chamber are known in the prior art, and include some draining and flushing features. These systems also enable the transfer roller to be cleaned by the doctor blade assembly as it cleans itself, shrinking the labor requirement of the cleaning and refilling process. It is highly desirable for an automated system to drain, flush, and clean all of the supply lines and fittings, whereby contamination from a former machine setup is removed before a new setup is created. One such system, depicted in U.S. Pat. No. 5,683,508 describes a doctor blade coating system which purports to automate the wash and clean cycle in addition to supplying the coating chamber. However, this system typifies the prior art in that it does not route the washing and flushing liquids through the same lines and fittings that deliver the ink or coating substances. As a result, some components such as the supply pump and supply lines, and the associated connectors are not cleaned before a new ink color or coating is introduced into the system.
It is also known that chambered doctor blade devices rely on doctor blades impinging on a transfer (anilox) roller to form a smooth and uniform film of ink or coating substance on the roller. The doctor blades are required to present a highly linear edge that impinges on the transfer roller with a force that is very uniform along the entire length of the blades (which can extend over 170 inches). Due to vibration and wear, the doctor blade edges may develop areas where the contact force varies along the length thereof, causing uneven distribution of the ink or coating film on the transfer roller.
There is known in the prior art at least one system for urging the doctor blades toward the transfer roller that employs hydraulic cylinders spaced along the apparatus to distribute the loading force therealong. Moreover, the hydraulic system is energized by pneumatic pressure, which provides hydrostatic compensation in the hydraulic circuit that enables each hydraulic piston to advance or retract as necessary to maintain a constant loading pressure against the transfer roller. In addition, the system provides a restricted flow orifice at each hydraulic cylinder, so that each cylinder may resist rapid motion (vibration and the like) while enabling slower adjustability in response to wear conditions. Although this superior doctor blade loading system has been available in the prior art, it has not been integrated into an automatic cleanup and ink and coating replacement system.
The present invention generally comprises a chambered doctor blade apparatus that provides automatic system for cleanup and replacement of ink or coating substance. The automatic system also operates a hydraulic head loading system that includes hydrostatic compensation, and integrates the head loading mechanism into the automated cleaning, flushing and replacement cycle. (Hereinafter, reference will be made to the use of ink in a printing process, but it is understood that any coating substance is encompassed by this discussion.)
In one aspect, the invention includes a chambered doctor blade assembly having a supply line connected to one end and a return line connected to the other end. A return pump has an intake connected to the return line, and an output connected through a return valve to a changeable ink reservoir. A supply pump has an output connected to the chamber supply line, and an intake connected through a supply valve to the ink reservoir. The supply pump intake line is also connected to a vent valve, and to a first wash valve that is connected to a first wash tank. The line from the supply valve at the ink reservoir is connected through a first pair of valves to a main water reservoir and a second wash tank. The line from the return valve at the ink reservoir is connected through a second pair of valves to the second wash tank and to a waste discharge outlet. Actuation of these valves and pumps in various combinations and sequences enables all of the valves, fittings, pumps, the doctor blade chamber, and the anilox roller to be drained, flushed, cleaned, flushed, and recharged with fresh ink.
In a further aspect of the invention, the system includes an automated system for controlling the valves and pumps enumerated above to carry out the cleaning and recharging functions also described above. The automated system includes a programmable logic controller (PLC) connected through a display driver to a touch screen display that depicts system conditions and presents an interactive graphical user interface for control purposes. The PLC is connected to a non-volatile memory that stores programming and values to carry out sequentially the required steps for cleaning, refilling, and running the chambered doctor blade assembly. The PLC is connected to each of the pumps and valves, and to the head loading valve of a hydrostatically compensated hydraulic head loading system.
The hydrostatically compensated hydraulic head loading system includes a hollow pivot tube extending parallel to the length of the doctor blade chamber and mounted on a coaxial pivot shaft. A plurality of hydraulic cylinders, each having a rolling diaphragm piston mounted therein, are spaced along the back panel of the doctor blade chamber, with each piston secured to the back panel. Each cylinder is rigidly secured to the pivot tube, whereby the pivot tube supports the hydraulic cylinders and the doctor blade assembly. A handle secured to the pivot tube permits the assembly to be rotated to bring the doctor blades into and out of engagement with the adjacent anilox roller.
The pivot tube also serves as a manifold to supply hydraulic fluid to the cylinders. An hydraulic supply reservoir includes a head space that is connected through a head loading valve to a source of selectively controlled pneumatic pressure, and the fluid is connected to supply the interior of the hollow pivot tube. An hydraulic supply line extends from each hydraulic cylinder to an adjacent fitting extending from the pivot tube to pressurize the cylinders whenever the head loading valve is activated. The pneumatic loading of the hydraulic fluid supplies a constant and uniform pressure to all the cylinders, and further enables the hydraulic fluid to flow bidirectionally and allows each hydraulic piston to advance or retract as necessary to maintain a constant loading pressure against the transfer roller. In addition, the system provides a restricted flow orifice at each hydraulic cylinder, so that each cylinder may resist rapid motion (vibration and the like) while enabling low velocity adjustability in response to wear conditions.